Copolyester fibers

ABSTRACT

The present invention provides a copolyester fiber consisting of a copolyester with primarily C 2-4  alkylene terephthalate units and a process for producing these copolyester fibers.  
     The copolyester contains more than 4 wt % up to 12 wt % poly(C 2-4  alkylene glycol) units and 60 to 260 ppm pentaerythritol units and/or a total of 150 to less than 2500 ppm carboxy methylene phosphonic acid units and/or carboxy ethylene phosphonic acid units polymerized into it.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention concerns a copolyester fiber consisting of acopolyester with mainly C₂-C₄ alkylene terephthalate units, poly(C₂-C₄alkylene glycol) units, and units derived from polyfunctional compounds(pentaerythritol and/or carboxy methylene phosphonic acid and/or carboxyethylene phosphonic acid), as well as a process for synthesis of thesecopolyester fibers by esterification, subsequent precondensation andpolycondensation of terephthalic acid with C₂-C₄ alkylene glycol,poly(C₂-C₄ alkylene glycol), and a polyfunctional compound as well asspinning the resulting polyester in the melt at spooling speeds of atleast 3000 m/min.

[0003] 2. Summary of the Related Art

[0004] Copolyester fibers are known. Examined German Patent No.1,266,922 discloses a process for producing fibers by melt spinning amodified polyester of terephthalic acid or isoterephthalic acid or thedimethyl esters thereof, ethylene glycol, 0.05 to 4.0 mol % alkoxypolyalkylene glycol and 0.05 to 2.4 mol % of a polyhydroxy compound suchas pentaerythritol. The fibers or filaments of this modified polyesterare essentially free of discoloration.

[0005] U.S. Pat. No. 5,756,033 describes a process for producing POYfibers from a polyester containing approximately 150 to 2500 ppm carboxyethylene phosphonic acid units. The polyester may also contain up to 10wt % other co-monomers, including polyglycols with a molecular weight ofless than 1000. This patent does not disclose any relationship to thedyeing properties of the fibers or how to optimize them.

[0006] U.S. Pat. No. 4,086,208 also describes a flame-retardantpolyester containing at most 10 mol % polyethylene glycol units and atleast 2500 ppm carboxy ethylene phosphonic acid units.

[0007] It is also known that fibers of polyesters can be pigmented withdisperse dyes. However, there are technical problems associated withdyeing because it is difficult for the large molecules of the dispersedyes to penetrate and diffuse into the amorphous portions of thepartially crystalline polyester. Fibers of unmodified polyethyleneterephthalate are therefore dyed at temperatures above 120° C. and underexcess pressure. However, it is also possible to add organic chemicalsthat penetrate like plasticizers into the polyethylene terephthalate,causing it to swell and thus making it more readily accessible for dyes.A disadvantage of this, however, is that the added organic chemicals areusually toxic substances that cause severe wastewater pollution.

[0008] International Patent Application WO 92/13120 discloses fine,non-delustered fibers that can be dyed at atmospheric pressure withoutchemical additives, the fibers consisting of a polyethyleneterephthalate containing 3.9 wt % polyethylene oxide and 0.175 wt %trimethylol propane which must not contain any delustering agents. Adisadvantage of these fibers with regard to uniform spinnability is thehigh trimethylol propane content. In addition, most applications requiredelustered fibers.

SUMMARY OF THE INVENTION

[0009] The present invention provides a copolyester fiber that can bedyed relatively easily with disperse dyes. The dyed fibers have arelatively high dye receptivity with minimal streakiness at the sametime. The invention also provides a process for producing saidcopolyester fibers.

[0010] The invention is described in greater detail below. All patentsand other publications are hereby incorporated by reference in theirentirety.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The polyester fibers of the invention are obtained bypolymerizing more than 4 wt % up to 12 wt % poly(C₂₋₄ alkylene glycol)units and 60 to 260 ppm pentaerythritol units and/or a total of 150 toless than 2500 ppm carboxy methylene phosphonic acid units and/orcarboxy ethylene phosphonic acid units into the copolyester. The amountsgiven in ppm are based on the total copolymer. It has surprisingly beenfound that by adjusting the quantity ranges of pentaerythritol units to60 to 260 ppm and/or of carboxy methylene and/or ethylene phosphonicacid units to a total of 150 to less than 2500 ppm, the dye receptivityof the copolyester fibers can be increased while there is a simultaneousreduction in streakiness. In this way it is also possible to avoid thedetrimental effects of using toxic substances (carriers) when dyeingfibers with disperse dyes.

[0012] In a preferred embodiment of this invention 80 to 200 ppmpentaerythritol units and/or a total of 500 to 750 ppm carboxy methylenephosphonic acid units and/or carboxy ethylene phosphonic acid units arepolymerized into the copolyester. According to another preferredembodiment of this invention, the amount of poly(C₂₋₄ alkylene glycol)units is 5 to 9 wt %. According to another preferred embodiment of thisinvention, the number average molecular weight of the polyalkyleneglycol units is between 200 and 3000 g/mol. When these quantity limitsare maintained, an optimum is achieved with respect to dyeingproperties, mechanical properties, and processing properties of thefibers.

[0013] The invention also comprises a process for producing acopolyester fiber, where more than 4 wt % up to 12 wt % poly(C₂₋₄alkylene glycol) with a number average molecular weight between 200 and3000 g/mol and 60 to 260 ppm pentaerythritol and/or a total of 150 toless than 2500 ppm carboxy methylene phosphonic acid and/or carboxyethylene phosphonic acid is added to the reaction mixture beforeprecondensation. The copolyester fibers produced by this process haveproven especially advantageous for dyeing with disperse dyes, yielding ahigh dye receptivity as well as low streakiness.

[0014] According to another embodiment of this invention,pentaerythritol and/or carboxy methylene phosphonic acid and/or carboxyethylene phosphonic acid and optionally a poly(C₂₋₄ alkylene glycol) areadded when 50% to 95% of the carboxyl groups of the dicarboxylic acid(s)of the esterification mixture are esterified. If addition of thesesubstances is postponed until this time, development of long chainbranching is guaranteed. This long chain branching leads to a change inthe viscoelasticity of the copolyester, i.e., the polyester melt becomescompressible, can absorb pressure variations, and dampens the fiberoscillations that occur during spinning, thus resulting in more uniformfibers. The degree of esterification (U) can be calculated from thesaponification number (V_(z)) and the acid number (S_(z)) of thereaction mixture according to the formula U=(V_(z)−S_(z))·100/V_(z). Thesaponification number is determined by saponification with potassiumhydroxide in n-propanol and potentiometric titration, and the acidnumber is determined by potentiometric titration in dimethyl formamide.

[0015] According to another especially optimal embodiment of thisinvention, the amount of poly(C₂₋₄ alkylene glycol) in the copolyesteris 5 to 9 wt %.

[0016] The quantity of pentaerythritol to be added is preferably 80 to200 ppm. In the case of carboxy ethylene phosphonic acid, preferably 500to 750 ppm is added. Mixtures of both branching components may be added,e.g., 50% pentaerythritol based on 80 to 200 ppm and 50% carboxyethylene phosphonic acid based on 500 to 750 ppm. If the quantity addedis too low, spinnability will be adequate, but the elongation of the POYfilaments spun at a high speed will be too low for draw texturing. Ifthe quantity added is slightly too high, the strength of the DTY yarnwill leave something to be desired, whereas if the quantity added issubstantially too high, the copolyester can no longer be spun well anduniformly. Pentaerythritol and carboxy phosphonic acid compounds areneither volatile nor do they form volatile compounds under theconditions of polyester synthesis, so the metered addition of thecompounds can be performed without concern for possible losses.Furthermore, there is no disturbance due to entrained pentaerythritol orcarboxy phosphonic acid compounds in recycling unpurified glycol (fromthe vapors from condensation).

[0017] According to another embodiment of this invention, the process isfollowed by further processing of the copolyester fibers by drawtexturing at speeds of at least 500 m/min. Since POY fibers from thecopolyester according to this invention, spun at a minimum speed of 3000m/min, have an elongation at break of at least 130%, they can beprocessed by draw twisting or preferably by draw texturing methods atspeeds of at least 500 m/min, preferably at least 600 m/min, withexcellent results to form DT or DTY yarn with a normal elongation(approx. 20-30%) and good strength (approx. 35 cN/tex or more). Theexcellent drawability of the POY fibers according to this inventionpermits up to approx. 15% higher spinning throughput by first spinningPOY fibers at a higher titer, which is then converted to the nominaltiter by a higher degree of drawing in the subsequent drawing operation.Reduced error incidence and increased productivity can even be achievedthrough further processing by weaving or warp knitting.

[0018] Melt spinning can be performed in any known way, e.g., by themethod according to U.S. Pat. Nos. 4,940,559 or 5,340,517. The polyestermelt can be spun directly after polycondensation or it may first begranulated and the granules melted again before spinning. Draw twistingand draw texturing are performed using conventional equipment,preferably with a high processing speed.

[0019] The polyester is produced in a known way by continuous ordiscontinuous direct esterification of terephthalic acid with C₂₋₄alkylene glycol and subsequent precondensation and polycondensation,wherein poly(C₂₋₄ alkylene glycol) and the branching component(s)preferably are added jointly or separately to the reaction mixturebefore precondensation, at the beginning of or during esterification,preferably when 50% to 80% of the carboxyl groups of thepolyester-forming dicarboxylic acid(s) are esterified. Condensation isperformed in the presence of conventional catalysts, such as antimony,titanium and/or germanium compounds. Delustering agents such as titaniumdioxide and optional coloring agents, bluing agents and/or stabilizersmay be added to the reaction mixture at any time during polyestersynthesis before spinning.

[0020] The alkylene groups of the C₂₋₄ alkylene glycol and those ofpoly(C₂₋₄ alkylene glycol) may be different or preferably the same. TheC₂₋₄ alkylene glycol is preferably ethylene glycol, and the poly(C₂₋₄alkylene glycol) is polyethylene glycol. A small portion of theterephthalic acid and/or the ethylene glycol may be replaced by otherdicarboxylic acids and/or diols, such as isophthalic acid,1,4-cyclohexane dicarboxylic acid, 2,6-naphthalene dicarboxylic acid,p-hydroxy benzoic acid, 4,4′-biphenyl dicarboxylic acid, adipic acid,diethylene glycol, 1,3-propane diol, 1,4-butane diol, 1,4-cyclohexanedimethanol. The amount of these comonomers should not exceedapproximately 10 wt % in the polyester because otherwise the fiberproperties differ too greatly from those of polyethylene terephthalatefibers. Polyethylene terephthalate is the preferred polyester.

[0021] The reaction mixture according to this invention undergoespolycondensation more rapidly than reaction mixtures without thebranching components, i.e., the desired final viscosity of the polyesteris achieved after a precondensation and polycondensation time that is upto 10% shorter. The accelerated effect with a subsequent optionalsolid-phase polycondensation is also greatly pronounced.

[0022] The object of this invention will be explained in greater detailon the basis of the following examples, which are intended forillustrative purposes only and are not intended, nor should they beconstrued, as limiting the invention in any manner. Those skilled in theart will appreciate that variations and modifications of the examplespresented below can be made without exceeding the spirit or scope of theinvention.

EXAMPLES Examples 1-3

[0023] 212 kg terephthalic acid, 88 kg ethylene glycol, 5.5 kg 2%antimony acetate solution in ethylene glycol were mixed togetherhomogeneously while stirring. The mixture was fed into an esterificationreactor preheated to approx. 265° C., filled approx. 30% withprecondensate of the preceding batch and 3 kg 25% titanium dioxidesuspension in ethylene glycol within approx. 140 minutes under normalpressure, and esterified for 30 minutes more at 265° C. and normalpressure, separating the reaction water. After 80% of the theoreticalquantity of reaction water had distilled off, 13.75 kg polyethyleneglycol (400) dissolved in 3.5 kg ethylene glycol was added to theesterification reactor. After adding 14 g phosphoric acid,precondensation was initiated as the pressure dropped slowly to 50 mbar(abs.) and the temperature was increased at the same time to approx.275° C. within 30 minutes. Approx. 15 minutes before the start of thegradual reduction in the reaction pressure, quantities ofpentaerythritol listed in the table below were added, in each case inthe form of a hot solution in 1 kg ethylene glycol. The precondensatewas fed through a 15 μm filter into the polycondensation reactor, thepressure lowered to less than 2 mbar (abs.) within 45 minutes, and theactual polycondensation performed at 280° C. according to the followingtable until reaching the desired intrinsic viscosity. Then the polyesterwas discharged from the polycondensation reactor within 20 minutes andgranulated. The granules were melted in a melt extruder, and the meltwas spun at approx. 295° C. through a 34-hole nozzle plate with a nozzlehole diameter of 0.25 mm. The fibers were cooled in a blow shaft withtransverse flow and then provided with a preparation (type Zimmer K105)and bundled, passed into a draw-off machine with a 9-fold looped pair ofgodet rollers and ultimately reeled up. The resulting POY fibers werethen draw textured with a friction texturing machine (model BARMAGFK6-S-900 with a 1-7-1 assembly ceramic disk (Ceratex C 0.85 and SPK-C0.85-M)) at temperatures of 195° C. and 160° C. of the first and secondheating elements, respectively, and a D/Y ratio 1:2.15 and 1:2.2.

Examples 4 and 5 (Comparative Examples)

[0024] In Examples 4 and 5, the same procedure was followed as inExamples 1 to 3, but no polyethylene glycol or pentaerythritol was addedin Example 4, and no pentaerythritol was added in Example 5. Theresulting POY fibers are characterized in particular by a lowerelongation, which has a detrimental effect on the texturing speed. Inaddition, the streakiness is increased in the absence ofpentaerythritol, and the dye receptivity is dramatically inferior in theabsence of polyethylene glycol.

[0025] The quantities used and the characteristic values obtainedaccording to Examples 1 through 5 are listed in the following table.Example no. 1 2 3 4 5 Esterification Polyethylene kg 13.75 13.75 13.75 —13.75 glycol Pentaerythritol g 38 50 62 — — Copolyester Intrinsicviscosity dL/g 0.65 0.63 0.67 0.65 0.66 Diethylene glycol wt % 0.8 0.80.8 0.7 0.8 POY yarn* Spooling speed m/ 3200 3200 3500 3200 3200 min

[0026] Example no. 1 2 3 4 5 Total titer dtex 139 139 128 292 292Elongation % 135 141 141 130 134 Strength cN/tex 21 20 17 23 22 DTYyarn* Texturing m/min 800 800 800 600 600 speed Drawing ratio 1: 1.731.74 1.68 1.72 1.74 Total titer dtex 84 81 80 179 177 Elongation % 26 2631 22 29.2 Strength cN/tex 38 37 30 40.2 37.7 Dye receptivity % 900 13001500 100 950 Streakiness level 2 2+ 2− 2 3

[0027] *POY=partially oriented yam

[0028] DTY=drawn and textured yam

[0029] The intrinsic viscosity was measured at 25° C. on a solution of500 mg polyester in 100 mL of a mixture of phenol and1,2-dichlorobenzene (3:2 parts by weight).

[0030] The diethylene glycol content was determined by gaschromatography in an ester exchange mixture of 1 g polyester with 30 mLmethanol and 50 mg/L zinc acetate prepared at 200° C. in a Carius tube.

[0031] The strength of the fibers and the elongation at break weredetermined at room temperature on a test length of 200 mm for POY and500 mm for DTY with a draw-off speed of 2000 mm/min in the case of POYor 1500 mm/min with DTY.

[0032] The dye receptivity was determined by producing a round knit tubeof fibers of the modified polyethylene terephthalate to be tested aswell as standard polyethylene terephthalate. This combined tube was dyedin a dyeing apparatus without a carrier for 30 minutes at 95° C. with 1%Terasil marine blue GRL-C 200% (Ciba Geigy, Switzerland), bath ratio1:50. The K/S value was determined from the reflectance R, which wasmeasured photometrically, by the following equation according to KubelkaMunk: $\frac{K}{S} = \frac{\left( {100 - R} \right)^{2}}{200R}$

[0033] The dye receptivity of the yam to be tested is obtained bycomparison with that of the standard material:

Dye receptivity (%)=[(K/S_(specimen))/(K/S_(standard))]·100%

[0034] The streakiness, i.e., irregularity in coloration of the dyedtube, was evaluated by passing the dyed tube over a test board andcomparing the streakiness with four corresponding standards. Level 1means “very good” (no streaking) and level 4 means “poor” (severestreaking).

We claim:
 1. A copolyester fiber with primarily C₂₋₄ alkyleneterephthalate units and containing more than 4 wt % up to 12 wt %poly(C₂₋₄ alkylene glycol) units and 60 to 260 ppm pentaerythritol unitsand/or a total of 150 to less than 2500 ppm carboxy methylene phosphonicacid units and/or carboxy ethylene phosphonic acid units.
 2. Thecopolyester fiber according to claim 1, wherein the copolyester contains80 to 200 ppm pentaerythritol units and/or 500 to 750 ppm carboxymethylene phosphonic acid units and/or carboxy ethylene phosphonic acidunits.
 3. The copolyester fiber according to claim 1, wherein the amountof poly(C₂₋₄ alkylene glycol) units is 5 to 9 wt %.
 4. The copolyesterfiber according to claim 1, wherein the number average molecular weightof the poly(C₂₋₄ alkylene glycol) units is between 200 and 3000 g/mol.5. The copolyester fiber according to claim 1, wherein the copolyesterfurther contain delustering agents, pigments, bluing agents, and/orstabilizers.
 6. The copolyester fiber according to claim 1, wherein theC₂₋₄ alkylene terephthalate units are ethylene terephthalate unitscontaining 0 to 10 wt % of units derived from other dicarboxylic acidsand/or diols, and the poly(C₂₋₄ alkylene glycol) units are polyethyleneglycol units.
 7. A process for producing a copolyester fiber, theprocess comprising fiber esterification, precondensation andpolycondensation of terephthalic acid with C₂₋₄ alkylene glycol,poly(C₂₋₄ alkylene glycol), and a polyfunctional compound and spinningin the melt of the resulting copolyester at spooling speeds of at least3000 m/min, wherein more than 4 wt % up to 12 wt % poly(C₂₋₄ alkyleneglycol) with a number average molecular weight between 200 and 3000g/mol, and as polyfunctional compound 60 to 260 ppm pentaerythritol,and/or a total of 150 to less than 2500 ppm carboxy methylene phosphonicacid and/or carboxy ethylene phosphonic acid are added to the reactionmixture before precondensation.
 8. A process according to claim 7,wherein the poly(C₂₋₄ alkylene glycol), pentaerytluitol and/or carboxymethylene phosphonic acid and/or carboxy ethylene phosphonic acid isadded when 50% to 95% of the carboxyl groups of the dicarboxylic acid(s)of the esterification mixture have been esterified.
 9. A processaccording to claim 7, wherein the quantity of poly(C₂₋₄ alkylene glycol)in the copolyester is 5 to 9 wt %.
 10. The process according to claim 7,wherein one or more delustering agents, coloring agents, bluing agentsand/or stabilizers are added to the reaction mixture at any time beforespinning.
 11. The process according to claim 7, wherein the C₂₋₄alkylene glycol is ethylene glycol, 0 to 10 wt % of the terephthalicacid and/or ethylene glycol is replaced by other dicarboxylic acidsand/or diols, and the poly(C₂₋₄ alkylene glycol) is polyethylene glycol.12. The process according to claim 7, wherein the copolyester fiber isprocessed further by draw texturing at a speed of at least 500 m/min.